Automotive type lead-acid batteries have interlaced positive and negative electrodes, also called plates. Each plate consists of special material, known as active material, supported on lead-alloy grids. The active material is formed from lead oxide pastes which are processed to a firm, porous form.
In the preparation of plates for a lead-acid battery, a mixture is formed containing oxides of lead, a significant amount of metallic lead, sulfuric acid, water and various other additives. As a result of chemical reaction during mixing, a portion of the mixture is initially converted to lead sulfate (PbSO.sub.4), providing an active material precursor paste which includes lead and its oxides and sulfates.
The precursor paste is applied to conductive lead grids and the freshly pasted plates are then typically cured to stabilize the precursor material and to enhance the strength. Both positive and negative plates are made by the same basic process except for the selection of additives.
Negative plates are cured for up to three days in a high humidity warm air atmosphere to oxidize the free lead. Positive plates are cured by steam at near 100.degree. C. for 3 hours. Plates are assembled in the battery and formed in a two-stage process which involves charging at a relatively high rate for 8 to 9 hours, until the temperature reaches 150.degree. F. to 170.degree. F. Batteries are then let stand for 2 to 3 hours and the charging completed at a lower current density for an additional 14 hours. This procedure normally results in plates which are in the range of 80 to 90% converted to metallic lead negatives and lead dioxide positives. The current process is highly dependent on timing and close control of the curing and charging stages. The charging process is also highly inefficient, requiring on the order of 250% of the calculated energy input to reach full charge.
Therefore, it is desirable to have a new type of active material for a lead-acid battery and a new process for forming plates with the new material.